Field of the Invention
[0001] This invention is related to molecular sieve catalysts and a method of making such
catalysts. In particular, the invention is directed to a method of preparing a slurry
containing molecular sieve using microfiltration. The invention is also directed to
converting an oxygenate to a product containing olefin by contacting the oxygenate
with the catalyst of the invention.
Background of the Invention
[0002] Olefins, particularly light olefins, have been traditionally produced from petroleum
feedstocks by either catalytic or steam cracking. Oxygenates, however, are becoming
an alternative feedstock for making light olefins. Particularly promising oxygenate
feedstocks are alcohols, such as methanol and ethanol, dimethyl ether, methyl ethyl
ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates
can be produced from a variety of sources including synthesis gas derived from natural
gas; petroleum liquids; carbonaceous materials, including coal; recycled plastics;
municipal wastes; or any appropriate organic material. Because of the wide variety
of relatively inexpensive sources, alcohol, alcohol derivatives, and other oxygenates
have promise as an economical, non-petroleum source for light olefin production.
[0003] One way of producing olefins is by the catalytic conversion of methanol using a silicoaluminophosphate
(SAPO) molecular sieve catalyst. See, for example, U.S. Patent Nos. 5,912,393 and
5,191,141 to Barger et al. U.S. Patent No. 4,499,327 to Kaiser, discloses making olefins
from methanol using SAPO molecular sieve catalysts. The process can be carried out
at a temperature between 300°C and 500°C, a pressure between 0.1 atmosphere to 100
atmospheres, and a weight hourly space velocity (WHSV) of between 0.1 and 40 hr
-1.
[0004] U.S. Patent No. 4,130,485 to Dyer et al. discloses a method of concentrating particulate
solids having a particle size distribution from about 0.1 to 50 microns using a solid,
porous, tubular microfilter. Wash water is added to the slurry while the slurry is
concentrated by the microfilter until the desired purity of slurry is obtained. The
addition of wash fluid is halted, and the slurry is further concentrated to a 11%
solid content.
[0005] U.K. Patent Application 1,356,741 discloses a method of concentrating biological
solids with at least two microfilters in series. The first microfilter consisted of
a pore size of 0.45 µm, and the second a 0.22 µm pore filter.
[0006] U.S. Patent No. 5,919,721 to Potter discloses the use of a microfilter to maximize
the amount of zeolite molecular sieve less than 1 µm in the concentrate. The initial
catalyst slurry contains solids with an average size of 0.3 microns and an initial
concentration of about 20% by weight solids. The concentrate of the final slurry is
about 40% by weight solids. After repetitive washings with wash fluid, the concentrate
is removed from the microfilter and dried by vacuum filtration.
[0007] U.S. Patent No. 5,126,308 suggests that SAPO molecular sieve with an average particle
diameter of which 50% are less than 1.0 µm and no more than 10% are greater than 2.0
µm lead to an increase in catalytic activity and selectivity. The laboratory prepared
SAPO is recovered by centrifugation, washed with water, dried, and formed into pellets.
[0008] Inui et al. in
Applied Catalysis, vol. 58, p. 155-163, 1990, shows that relatively small SAPO-34 particles can be prepared
by what is known as a rapid crystallization method. This method produces SAPO-34 particles
in the range of 0.5 to 2 µm. The laboratory prepared SAPO is washed with water, recovered
by centrifugation and dried.
[0009] After the molecular sieve particles are prepared, the molecular sieve particles must
be separated from its preparation mixture or crystallization solution. Conventional
laboratory-scale separation procedures include centrifugation and pressure filtration.
However, both of these methods prove to be impractical for commercial-scale production
of molecular sieve particles. A large-scale centrifugation process, because of the
capital and operational costs, is economically impractical. In the case of pressure
filtration, the smaller particles form a compacted filter cake on top the filter medium.
The result is a significant decrease in flux rate of wash fluid across the filter
cake and through the pores of the filter which leads to long processing times. Also,
channels may develop in the filter cake which allows the wash fluid to pass trough
the filter cake without contacting most of the molecular sieve particles. As a result,
the molecular sieve is inadequately washed, and contaminants from the preparation
mixture are incorporated into the catalyst.
[0010] The formation of the compacted filter cake also leads to very high pressure drops
across the filter medium, which may result in failure of the filtering medium. Most
pressure filters are designed to withstand a maximum pressure drop of about 75 psi.
The pressure drop across a bed of solids is proportional to the mass flow of the filtrate
through the filter, filtrate viscosity (thus, hot water is often used to reduce viscosity),
cake thickness, and cake resistance. Cake resistance is inversely proportional to
the square of the effective particle diameter, and proportional to the porosity of
the cake. As an example, a pressure drop across a bed of 0.3 micron diameter solids
will be at least 16 times that of a pressure drop across a bed of 1.2 microns diameter
solids, due to smaller particle size, assuming all other properties are equal. Further,
since these smaller sized particles are more compressible, the void volume (related
to bed porosity) also decreases, resulting in even more increase in pressure drop.
Accordingly, conventional filtration processes becomes very difficult because of these
large pressure drops across beds of small particles.
[0011] Novel methanol-to-olefin (MTO) catalysts are needed which exhibit a high ethylene
and propylene selectivity, an increase resistance to coking, or an increase in resistance
to attrition. Catalysts with relatively small, average particle size molecular sieve
could provide significant steps in one or all three of these areas of catalyst development.
However, present methods of isolating commercial-scale quantities of these smaller
molecular sieve particles from their preparative solutions, such as by centrifugation
or pressure filtration, is either too costly and/or very inefficient. Methods to effectively
recover small, molecular sieve particles, and a method of incorporating them into
catalyst are needed.
Summary of the Invention
[0012] This invention is directed to a molecular sieve catalyst wherein the molecular sieve
is washed and concentrated as a slurry from a preparation mixture using a microfiltration
process. The permeate from the microfiltration process has a conductivity from 50
µmho/cm to 5000 µmho/cm. The catalyst contains molecular sieves selected from aluminophosphates,
metal-aluminophosphates, silicoaluminophosphates, metal-silicoaluminophosphates, and
mixtures thereof. Preferably, the catalyst comprises molecular sieves comprising SAPO-17,
SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-47, ALPO-5, ALPO-11, ALPO-18, ALPO-34, ALPO-36,
ALPO-37, ALPO-46, metal containing forms of each thereof, or mixtures thereof in the
amount from 10% to 60% by weight based on the weight of calcined catalyst. The molecular
sieve catalyst also contains a binder, preferably silica, silica-alumina, or alumina,
present in the amount from 5% to 20% by weight based on the weight of uncalcined catalyst,
and optionally a matrix material, preferably at least one clay, more preferably kaolin,
present in an amount from 30% to 90% by weight based on the weight of calcined catalyst.
[0013] The invention is a process for making a catalyst, comprising
i) preparing a concentrated molecular sieve slurry containing molecular sieve and
a fluid by the process comprising,
a) introducing a molecular sieve slurry containing molecular sieve particles, the
preparation mixture and a fluid into the front end of at least one microfilter channel
comprising pores;
b) passing the slurry through the microfilter channel and separating the permeate
passing through the pores of the microfilter channel to concentrate the slurry; and
c) recovering a concentrated molecular sieve slurry from the back end of the microfilter
channel;
ii) mixing the concentrated molecular sieve slurry with a binder to form a catalyst
slurry;
iii) directing the catalyst slurry to a forming unit;
iv) recovering catalyst particles.
[0014] Preferably, the fluid in the starting molecular sieve slurry is water. In an embodiment
of the invention, the process further comprises the steps of d) adding wash fluid
to the molecular sieve slurry, e) mixing the molecular sieve slurry and the wash fluid
in a holding tank, f) injecting the molecular sieve slurry through the front end of
at least one microfilter channel comprising pores and separating the permeate passing
through the pores of the microfilter. Steps d), e) and f) may be repeated until the
molecular sieve slurry has the desired purity level, conveniently until the permeate
passing through the pores has a conductivity of 50 µmho/cm to 5000 µmho/cm.
[0015] Preferably, the wash fluid is water, an alcohol, or a mixture thereof. Steps d),
e) and f) may be performed continuously. In order to backwash the microfilter, the
wash fluid may contact the molecular sieve slurry from the backside of the microfilter
channel.
[0016] Adding of the wash fluid may be performed as the molecular sieve slurry is concentrated.
The permeate separated at steps b) and/or f) can be concentrated with a nanofilter
to give a concentrated permeate and is used in a process for the manufacture of a
molecular sieve. The nanofilter typically contains a porous material with nominal
pore diameter of 0.5 to 10 nanometers.
[0017] The molecular sieve slurry used in step a) can be the permeate of the filtration
of a molecular sieve preparation mixture using a macrofilter, typically with a nominal
pore opening of greater than 10 microns.
[0018] The process includes preparing a molecular sieve slurry containing molecular sieve
and at least one fluid. The molecular sieve is mixed with a binder, and optionally
a matrix material to form a catalyst slurry. The catalyst slurry is then directed
to a forming unit, preferably a spray dryer, to produce the catalyst. The catalyst
slurry preferably has a total solid content from 30% to 50% by weight.
[0019] The process of preparing the molecular sieve slurry includes concentrating the molecular
sieve from a preparation mixture with a microfilter; washing the molecular sieve and
any of the remaining preparation mixture with a wash fluid; arid concentrating the
molecular sieve from the wash fluid and any remaining preparation mixture with the
microfilter. The process may also include concentrating a premeate with a nanofilter,
the permeate obtained from concentrating the molecular sieve, and returning at least
a portion of the concentrated permeate to a process stream used in the preparation
of the molecular sieve. The microfilter pressure drop across the porous walls of the
microfilter is preferably from 10 psi to 80 psi, more preferably from 15 psi to 50
psi. The temperature of the molecular sieve slurry is preferably maintained at a temperature
from 10 °C to 90 °C, more preferably from 30 °C to 60°C.
[0020] In some cases it is not necessary to concentrate the molecular sieve from the preparation
mixture prior to adding the wash fluid. Instead, the wash fluid is added to the molecular
sieve and preparation mixture before the molecular sieve is concentrated by the microfilter.
In other cases, the molecular sieve may be concentrated from the preparation mixture
prior to adding the wash fluid by using conventional filtration techniques, or using
a microfilter with a pore size greater than 10 microns.
[0021] The invention is also directed to a method of making ethylene and propylene by contacting
the molecular sieve catalyst of the invention with an oxygenate under conditions to
convert the oxygenate. Preferably, the oxygenate is selected from methanol, dimethyl
ether and mixtures thereof. Also preferably, the molecular sieve present in the catalyst
used in the method of making ethylene and propylene is SAPO-34, SAPO-18, ALPO-18 or
mixtures thereof.
Brief Description of the Drawings
[0022] The invention will be better understood by reference to the Detailed Description
of the Invention when taken together with the attached drawings, wherein:
Figure 1 is a cross-section of a porous filter channel during the filtration process
in the microfilter;
Figure 2 is a cross-section of the microfilter with a plurality of porous filter channels;
and
Figure 3 depicts a block diagram of the microfiltration system of the invention.
Detailed Description of the Invention
[0023] This invention overcomes many of the problems associated with small particle filtration
by using a microfiltration process. The microfiltration process provides a method
to separate and wash the molecular sieve from the preparation mixture without isolating
the molecular sieve particles in its dry form. The molecular sieve, preferably with
an average particle diameter of less than 5 microns, is washed and separated from
the other chemical components in the preparation mixture as a molecular sieve slurry
with a selected solid content and a selected purity level of the molecular sieve slurry
fluid. The molecular sieve is not collected as a dried solid. The molecular sieve
slurry is then combined with other formulating components of the catalyst, such as
binders and/or matrix materials, to form a catalyst slurry. Prior to mixing with the
molecular sieve slurry the formulating components may exist as dry or semi-wet solids
or as slurries. The catalyst slurry is then directed to a forming unit selected from
an extrusion unit, a pelletizing unit, or a spray dryer. It is preferred that the
catalyst slurry be spray dried.
[0024] The microfiltration process may include a batch process, a semi-batch process, or
a continuous process to concentrate and separate the molecular sieve from the preparation
mixture or crystallization solution. In the batch process a given amount of preparation
slurry containing molecular sieve and the other components of the preparation mixture
is added to a holding tank. The components in the preparation mixture include the
solvent used in the synthesis or recrystalization, as well as unreacted template,
e.g., tetraethylammonium hydroxide (TEOH), dipropylamine (DPA), and aluminum, silicon,
and phosphorous containing chemical components. The initial solid content of molecular
sieve in the preparation slurry is approximately between 5% and 30% by weight. The
preparation slurry is directed to a filter, and a portion of the preparation mixture
is separated from the slurry as the preparation mixture passes through the pores of
the filter.
[0025] The filter used to initially concentrate the molecular sieve from the preparation
mixture may be a conventional macrofilter or a microfilter. If a macrofilter is used,
the permeate from the macrofilter is directed to the microfiltration process to further
separate the relatively small molecular sieve particles that passed through the pores
of the macrofilter with the preparation mixture. The molecular sieve collected with
the macrofilter is filtered and washed using conventional methods, such as pressure
filtration. This molecular sieve can be combined with the molecular sieve slurry obtained
from the microfiltration process prior to the addition of binder and/or matrix material.
If a microfilter is used, the molecular sieve is partially separated or concentrated
from the preparation mixture by passing the preparation slurry through the channels
of the microfilter, a given amount of wash fluid is added, the molecular sieve slurry
and wash fluid is mixed in a holding tank, and the microfiltration is repeated. The
steps of washing and partially filtering are repeated until the permeate passing through
the pores of the microfilter is of a desired purity level. The purity level in the
permeate, i.e., the amount of unwanted chemical components in the permeate, indicates
the proportion of the chemical components contained in the molecular sieve slurry.
It is preferred that the molecular sieve is washed with wash fluid until the permeate
has a conductivity of 50 µmho to 5000 µmho. The molecular sieve slurry containing
molecular sieve, about 20% to 50% by weight, and wash fluid, preferably water, an
alcohol, or a mixture thereof, is then directed to a catalyst formulation process.
The wash fluid may contact the molecular sieve slurry from the backside of the microfilter
so as to remove a portion of filter cake from the wall of the porous filter channel.
This cake removal process is commonly referred to as "back washing."
[0026] It is to be understood by one skilled in the art, that the batch process of the invention
described above can be practiced in other ways. For example, the preparation slurry
from the synthesis can be mixed with a portion of wash fluid prior to concentrating
the molecular sieve. Also, the invention is adaptable to a continuous process, such
that the preparation slurry is directed to a holding tank. From the holding tank,
the preparation slurry is directed to the microfilter while wash fluid is added. The
rate of preparation slurry added to the process of the invention is related to the
rate of molecular sieve slurry removed from the process, the rate of wash fluid added,
and the desired steady-state level of chemical components in the permeate.
[0027] The process of the invention may include concentrating the permeate from the microfilter
with a nanofilter. Some or all of the concentrated permeate can then be recycled to
a process stream used in the preparation of the molecular sieve. The term "permeate"
is defined in the specification as any proportion of preparation mixture and/or wash
fluid that is collected after having passed through the pores of the microfilter from
any one or all of the concentrating steps in the process of the invention.
[0028] The term "particle" is defined in the specification as any molecular solid having
a dimensional volume. The molecular solid can be crystalline or amorphous, or may
have portions that are crystalline and other portions amorphous. The molecular solid
can be a single crystal, or an agglomerate of single crystals and or a mixture of
single crystals and amorphous solids.
[0029] The term "microfilter" is defined as a device having a porous material with nominal
pore opening of about 0.05 micron to 10 microns. The term "nanofilter" is defined
as a device having a porous material with nominal pore opening of about 0.5 nanometer
to 10 nanometers. The term "macrofilter" is defined as a device having a porous material
with nominal pore opening of greater than 10 microns. The porous materials used in
the microfilters and nanofilters are generally known in the art and include, but are
not limited to, polymers, ceramics, and sintered metals. The pore size of the microfilter
should be less than the average particle size of the molecular sieve, however this
is not required. A microfilter having a pore size greater than the average particle
size of the molecular sieve will generally collect most of the smaller particles.
[0030] The slurry containing the molecular sieve, the wash fluid, and any remaining preparation
mixture contains 20% to 60% by weight, preferably 25% to 40% by weight of the molecular
sieve. After the molecular sieve has been washed to the desired point and collected,
the process may include mixing a matrix material with the molecular sieve prior to,
with, or following the mixing of the binder with the molecular sieve. Preferably,
the matrix material comprises at least one clay, more preferably kaolin clay, and
is present in the amount from 30% to 90% percent by weight based on the weight of
calcined catalyst. Preferably, the binder comprises silica, silica-alumina or alumina
present in the amount from 5% to 20% by weight based on the weight of calcined catalyst.
Typically, if alumina is to be incorporated as a binder, the source of the alumina
is peptized alumina or aluminum chlorhydrol. The aluminum chlorhydrol is converted
to alumina following heating of the prepared catalyst.
[0031] Fig. 1 depicts a cross-section of a porous microfilter channel
20 as the molecular sieve slurry
30 is being concentrated. The molecular sieve slurry includes the preparation mixture,
which contains the chemical components from the synthesis dissolved or suspended in
an aqueous liquid
21 and the molecular sieve particles
22, which flow along the length of the channel
20. The walls
24 of the channel
20 are porous and some of the preparation mixture passes through the walls
24, as depicted by the arrows
26, while the molecular sieve particles
22 are retained inside the channel
20. The pore size of the filter channel
20 is selected to retain the desired size of particles
22. As a result, particles
22 larger than the pore size of the channel
20 do not pass through the walls
24 of the channel
20, while preparation mixture in the aqueous liquid
21 and small sized particles that are much smaller than the pore size pass through the
walls
24 of the channel
20. High mass flux rates parallel to the surface of the filter channel
20 minimizes the buildup of molecular sieve particles from clogging the pore surface
of the filter channel
20.
[0032] It is to be understood that although Fig. 1 depicts the slurry
30 flowing in the interior portion of the channel
20, the process of the invention can also be practiced with the slurry
30 flowing along the outside surface of the channel and the permeate entering the interior
portion.
[0033] A microfilter 18 is shown in Fig. 2. The microfilter
18 may consist of a bundle of filter channels
20 having fibered, porous walls
24 as shown in Fig. 2. Slurry, not shown, is injected into one end of a channel
20 and removed from the opposite end of the channel
20. The microfilter
18 is similar in construction and appearance to a conventional single-pass shell and
tube heat exchanger. Alternatively, the microfilter can consist of a bundle of sintered
ceramic or metal channels with a well defined pore size. Generally, microfilters are
made out of a variety of materials including, but not limited to, polymers (such as
cellulose acetate), sintered metal, or ceramics. Also, the invention is not limited
to the use of a cylindrical microfilter. Other geometrically shaped microfilters can
be used, such as flat sheets or spiral wound sheets.
[0034] This invention differs from conventional microfiltration or ultrafiltration methods
because of the high solid content present in the slurry
30, shown in Fig. 1. Preferably, the invention processes slurry
30 with 5% to 60%, more preferably 5% to 40% percent by weight molecular sieve particles
22. The invention concentrates and washes large volumes of slurry
30 containing large amounts of particles
22. The washed and concentrated molecular sieve slurry is then mixed with binder and/or
matrix material to produce a molecular sieve catalyst slurry, which is directed to
a forming unit and processed into catalyst. The portions of the permeate can be discarded,
recycled, concentrated and recycled, or any combination thereof.
[0035] The microfiltration process of the invention can be a batch process with a given
amount of slurry to be washed and concentrated in slurry feed tank
28, as shown in Fig. 3. Alternatively, one of ordinary skill in the art would recognize
that a batch process can be modified with input streams, output streams, and optionally
a recycle stream, thereby converting the batch process shown in Fig. 3 to a continuous
flow process. As shown, the system has two fluid loops; a slurry feed loop and a wash
fluid loop (enclosed by dotted lines). The slurry loop circulates the slurry
30 through the microfilter
18 and back to the slurry tank
28. The wash fluid loop circulates wash fluid or back wash to the microfilter
18 and the slurry feed tank
28. In the slurry loop, the slurry
30 is directed from the slurry feed tank
28 to a pump
31 and then to the microfilter
18. Following passage through the porous filter channels
20, the slurry
30 is recycled back to the slurry feed tank
28 via stream
50.
[0036] Typically flow rates for conventional microfiltration are about 250 L/min per m
2 of tube cross-section, if 1 mm diameter channels are used. However, because molecular
sieve slurries are very viscous, slurry feed rates are limited to 10 to 60 L/min per/m
2 of tube cross-sectional area, preferably from 15 to 35 L/min per m
2, to avoid overpressuring the filter channels near the inlet of the microfilter. The
highest slurry feed rate is determined by the mechanical integrity of the microfilter
18, particularly the mechanical integrity of the filter channel walls
24. The inlet portion of the filter tubes must be able to mechanically withstand the
high pressure associated with high feed rates without partial or complete physical
disintegration due to excessive pressure drop across the walls
24 of the channels
20 at the inlet end. At very low slurry feed rates the minimum pressure drop across
the wall
24 near the outlet of the microfilter
18 is 15 to 30 psi. The corresponding pressure drop across the walls
24 near the inlet of the microfilter
18 is 30 to 50 psi. Higher pressure drops will generally facilitate the rate of filtration,
however, the higher pressure drops may also necessitate the use of stronger filter
elements.
[0037] The pressure in the filter channel
20 may be controlled by a pressure control valve
36 at the discharge end of the microfilter
18 and measured by pressure indicator
302. The pressure drop in the channels
20 along the length of the channels
20 depend on the flow rate. The pressure drop increases with increasing flow rate, which
may be adjusted by a flow control valve
37 positioned on the inlet side of the microfilter
18. In addition, valve
38 may be employed to partially recirculate slurry
30 to the slurry tank
28. Thus, valves
37 and
38 control the flow rate entering the microfilter
32. The pressure drops at the inlet and outlet ends of the microfilter
32 are interrelated, and for a given process and microfilter adjustment of one may require
appropriate adjustment of the other. For example, if the slurry flow rate is increased
the outlet back pressure should be lowered.
[0038] The pore size is selected to prevent virtually all particles larger than a desired
size from passing through or permeating the porous wall
24 of the filter channel
20. The pore size of the microfilter
18 is based upon the average particle size of the molecular sieve and is preselected
to retain the smallest desired particles. The aqueous liquid which passes through
the walls
24 comprises the permeate stream
33; this permeate stream
33 is analogous to a filtrate stream in a pressure filtration process and is collected
in tank
34. The pressure (measured by pressure indicator
301) maintained on a fluid injected into the filter microfilter
18 supplies the pressure drop needed to force some of the permeate (preparation mixture
and/or wash fluid) through the walls
24 on each pass. The pressure across the porous walls
24 must be high enough to force permeate through the walls
24 but not so high as to over pressure and distort or tear the walls
24. Usually, a fluid circulating pump
31 and motor
35 provide this positive pressure. The opposite side or back end of the channel
20 is at ambient pressure and is connected to a means for collecting permeate which
is then directed to tank
34. Alternatively, the back end of the channel
20 may be placed under a partial vacuum or exposed to a pressure above atmospheric pressure.
[0039] It is possible during microfiltration (or ultrafiltration) for a high concentration
of solids to congregate near the surface of the walls
24 thus reducing permeate flow. Thus, for a constant flow rate, increasing the pressure
drop across the wall
24 of the channel
20. This is known as "concentration polarization". When this occurs, the microfilter
18 is back washed with wash fluid to reduce the concentration of solids near the inside
wall of the channel
20. Back washing is done using the back wash fluid in container
39, via pump
40 and valve
41, as shown in Fig. 3. The back washing aids in the removal of particles concentrated
along the inside wall of the microfilter
18. It is often desirable to maintain a constant concentration of slurry
30 in the slurry feed tank
28. This requires a source of make-up fluid from container
39, via pump
40 and valves
42 and
43, to replace any fluid lost from the slurry
30 via the permeate stream
33. Thus, the back wash loop is also used to provide make-up fluid and any make-up fluid
is preferably heated.
[0040] The process of concentrating the permeate (shown as process
46 in Fig. 3) collected in tank
34 is very similar to the process of concentrating the slurry
30. However, because the solid contents of the permeate is very low, significantly less
amounts of back wash, if any, is added from stream
45 to the process
46. The permeate from tank
34 is pumped to a nanofilter positioned within process
46. The nanofilter can be made from organic or inorganic components, for example, polymers,
sintered metal, ceramics, or composites thereof. In much the same way the pressures
and flow rates are controlled by a series of flow valves and pressure valves. The
concentrated permeate is recycled back to tank
34. The permeate from the nanofilter is collected in tank
48. Portions of the concentrated permeate can be recycled back to the sieve synthesis
unit to reduce material costs, or treated and properly discarded. The second permeate
resulting from the nanofiltration process can also be recycled in the process of the
invention, the synthesis unit, or disposed of.
[0041] The detailed batch process for washing and recovery of a molecular sieve slurry by
microfiltration (or ultrafiltration) in accordance with the teachings of the present
invention is as follows:
1. A batch of molecular sieve particles recovered from the preparation mixture are
slurried in wash fluid, preferably water. However, it may at times be necessary to
concentrate the preparation mixture and particles from the synthesis process if relatively
low yields of molecular sieve are obtained in the synthesis. Alternatively, portions
of the preparation mixture may be removed by vacuum applications with or without heating.
The slurry from the process synthesis may also be pre-filtered using conventional
methods to remove the relatively larger molecular sieve particles prior to directing
the slurry to the microfilter.
2. Although optional, preferably, the slurry is initially concentrated to approximately
30 percent by weight solids by microfiltering without adding any wash fluid or back
wash to the slurry. This initial concentration step reduces the amount of wash fluid
needed in subsequent steps by removing the majority of contaminants contained in the
preparation mixture. An initial slurry flow rate of 10 to 60 (or more) L/min per m2 of cross-sectional entry area of the filter cartridge and preferably 20 to 30 L/min
per m2 may be established. This flow rate is reduced with time to maintain an acceptable
pressure drop across the microfilter's walls at the inlet and outlet of the hollow
fibers as the slurry concentrates. The initial concentration step is stopped when
the pressure exceeds a preselected maximum pressure allowed across the filter media,
such as for example, 15 psi across the wall for a particular filter unit that has
a maximum pressure limitation of 20 psi. The maximum across-the-wall pressure is an
operating characteristic of a particular filter and is determined by the manufacturer
of the filter cartridge; thus, the slurry is concentrated to some maximum concentration
functionally related to the operating characteristics of the filter. The filter may
be back flushed with a minimum amount of wash fluid to remove a portion of the filter
cake from the walls and then, optionally, the concentration is continued. Any number
of such back washing steps may be employed during the initial concentration step.
A final back wash may be performed after the final, initial concentration step is
completed.
3. Once the concentration step is completed, a make-up fluid flow is started that
matches permeate flow through the microfilter. This is the washing step of the process.
The feed rate is gradually increased to maintain a preselected pressure across the
filter walls as contaminants are removed, such as for example about 10 psi for a filter
unit with a maximum pressure limitation of 20 psi. As permeate flow rate increases,
the makeup fluid feed rate is increased.
Alternatively, "washing" of the molecular sieve particles may be accomplished by
repeating the concentration step followed by a back washing step a sufficient number
of times to achieve the desired molecular sieve slurry composition.
[0042] The final concentration based upon the across-the-wall pressure limit of the filter
unit is typically 20 wt% to 60 wt % slurry concentration for current non-metallic
or non-ceramic cartridges. The filter is run at its maximum across-the-wall pressure
until no more permeate is discharged and the wash or concentration step is then stopped.
Again, this maximum concentration is functionally related to an operating characteristic
of the filter. However, higher solids contents may be achievable with different microfiltration
equipment and microfilters. The final solids concentration will be determined by the
mechanical strength (maximum pressure limit across the wall) of the filter used, the
ability of the pumping system to pump the thickened slurry, and the slurry components.
[0043] To determine when the slurry has been adequately washed with wash fluid, and thus
ready for the addition of other catalyst components, the chemical or physical properties
of the permeate are measured. For example, the conductivity or density of the permeate
can be measured. The degree of washing will depend upon the intended use of the molecular
sieve slurry. It is preferred that the conductivity of the permeate be 50 µmho to
5000 µmho prior to making the catalyst slurry.
[0044] Temperature of the molecular sieve slurry has a significant effect on the flow rate
of the permeate through the pores of the microfilter. The temperature is preferably
maintained below 75 °C with a preferred temperature of 55 °C to 65 °C. In general,
the higher the temperature of the molecular sieve slurry, the lower the viscosity
of the slurry. This means permeate flow rate is higher at any given pressure differential
across the hollow fibers or alternatively, pressure may be reduced while maintaining
a constant permeate flow rate. Higher final slurry concentrations are achieved at
higher temperatures, but the slurry temperature should be maintained below the boiling
point of the fluid, and may be further limited by the necessity of maintaining the
temperature below any temperature limit imposed by the relative stability of the chemical
components of the slurry as well as the materials of the microfilter.
[0045] For a commercial process the volumes/areas/pore size of the microfilter
18, flow rates, and temperatures all are appropriately selected based upon the desired
unit capacity, slurry properties and equipment specifications. The maximum allowable
pressure for the microfilter
18 is determined by the microfilter manufacturer. Microfilters are commonly operated
at pressures of 1 psi to 50 psi, although higher pressure microfilters can be used
in the process. A parallel bank of microfilters
18 may be employed to increase the volume of slurry to be concentrated. A suitable slurry
recirculating pump
40 is selected, as is a flow controller
37 and back pressure regulator
36. This system also has a means for back washing, permeate removal, and slurry transfer
to and from the microfiltration process, as well as a slurry processing unit, such
as a spray dryer. Further, appropriate process instrumentation and controls may be
included to automate the process.
[0046] An optional second filtration step may be employed. If used, this portion of the
apparatus can be used to further separate components in the permeate collected in
vessel
34 described as part of the first stage filtration. A nanofilter, can be used to separate,
for example, water, from inorganic or organic components present in the first permeate
stream
33. Nanofiltration membranes are generally considered to be materials with pore openings
of 0.5 nanometer to 10 nanometers. Operation is in general similar to the operation
of the microfiltration except that typically nano-filtration cartridges are more efficiently
used at 40 psig to 200 psig.
[0047] The preferred molecular sieve catalyst used in the invention is one that incorporates
a silicoaluminophosphate (SAPO) molecular sieve. The molecular sieve comprises a three-dimensional
microporous crystal framework structure of [SiO
2], [AlO
2] and [PO
2] corner sharing tetrahedral units. It is preferred that the silicoaluminophosphate
molecular sieve used in this invention have a relatively low Si/Al
2 ratio. In general, the lower the Si/Al
2 ratio, the lower the C
1-C
4 saturates selectivity, particularly propane selectivity. A Si/Al
2 ratio of less than 0.65 is desirable, with a Si/Al
2 ratio of not greater than 0.40 being preferred, and a Si/Al
2 ratio of not greater than 0.32 being particularly preferred. A Si/Al
2 ratio of not greater than 0.20 is most preferred.
[0048] Silicoaluminophosphate molecular sieves are generally classified as being microporous
materials having 8, 10, or 12 membered ring structures. These ring structures can
have an average pore size from 3.5 to 15 angstroms. Preferred for MTO conversion are
the small pore SAPO molecular sieves having an average pore size of less than 5 angstroms,
preferably an average pore size ranging from 3.5 to 5 angstroms, more preferably from
3.5 to 4.2 angstroms. These pore sizes are typical of molecular sieves having 8 membered
rings.
[0049] The [PO
2] tetrahedral units within the framework structure of the molecular sieve of this
invention can be provided by a variety of compositions. Examples of these phosphorus-containing
compositions include phosphoric acid, organic phosphates such as triethyl phosphate,
tetraethylammonium phosphates, and aluminophosphates. The phosphorous-containing compositions
are mixed with reactive silicon and aluminum-containing compositions under the appropriate
conditions to form the molecular sieve.
[0050] The [AlO
2] tetrahedral units within the framework structure can be provided by a variety of
compositions. Examples of these aluminum-containing compositions include aluminum
alkoxides such as aluminum isopropoxide, aluminum phosphates, aluminum hydroxide,
sodium aluminate, and pseudoboehmite. The aluminum-containing compositions are mixed
with reactive silicon and phosphorus-containing compositions under the appropriate
conditions to form the molecular sieve.
[0051] The [SiO
2] tetrahedral units within the framework structure can be provided by a variety of
compositions. Examples of these silicon-containing compositions include silica sols
and silicium alkoxides such as tetra ethyl orthosilicate. The silicon-containing compositions
are mixed with reactive aluminum and phosphorus-containing compositions under the
appropriate conditions to form the molecular sieve.
[0052] Substituted SAPOs can also be used in this invention. These compounds are generally
known as MeAPSOs or metal-containing silicoaluminophosphates. The metal can be alkali
metal ions (Group IA), alkaline earth metal ions (Group IIA), rare earth ions, and
the additional transition cations of Groups IVB, VB, VIB, VIIB, VIIIB, and IB. Preferably,
the Me represents atoms such as Zn, Mg, Mn, Co, Ni, Ga, Fe, Ti, Zr, Ge, Sn, and Cr.
These atoms can be inserted into the tetrahedral framework through a [MeO
2] tetrahedral unit. Incorporation of the metal component is typically accomplished
adding the metal component during synthesis of the molecular sieve. However, post-synthesis
treatments such as impregnation or ion exchange can also be used. In post synthesis
ion exchange, the metal component will introduce cations at the surface of the molecular
sieve, not into the framework itself.
[0053] Suitable silicoaluminophosphate molecular sieves include SAPO-5, SAPO-8, SAPO-11,
SAPO-16, SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37, SAPO-40,
SAPO-41, SAPO-42, SAPO-44, SAPO-47, SAPO-56, the metal containing forms thereof, and
mixtures thereof. Preferred are SAPO-17, SAPO-18, SAPO-34, SAPO-35, SAPO-44, and SAPO-47,
particularly SAPO-18 and SAPO-34, including the metal containing forms thereof, and
mixtures thereof. As used herein, the term mixture is synonymous with combination
and is considered a composition of matter having two or more components in varying
proportions, regardless of their physical state.
[0054] Another embodiment of the present invention comprises concentrating an aluminophosphate
(ALPO) molecular sieve catalyst by microfiltration. Aluminophosphate molecular sieves
are crystalline microporous oxides which can have an AlPO
4 framework. They can have additional elements within the framework, typically have
uniform pore dimensions ranging from about 3 angstroms to about 10 angstroms, and
are capable of making size selective separations of molecular species. More than two
dozen structure types have been reported, including zeolite topological analogues.
A more detailed description of the background and synthesis of aluminophosphates is
found in U.S. Pat. No. 4,310,440, which is incorporated herein by reference in its
entirety. Preferred ALPO structures are ALPO-5, ALPO- 11, ALPO-18, ALPO-31, ALPO-34,
ALPO-36, ALPO-37, and ALPO-46.
[0055] The ALPOs can also include a metal substituent in its framework. Preferably, the
metal is selected from the group consisting of magnesium, manganese, zinc, cobalt,
and mixtures thereof. These materials preferably exhibit adsorption, ion-exchange
and/or catalytic properties similar to aluminosilicate, aluminophosphate and silica
aluminophosphate molecular sieve compositions. Members of this class and their preparation
are described in U.S. Pat. No. 4,567,029, incorporated herein by reference in its
entirety.
[0056] The metal containing ALPOs have a three-dimensional microporous crystal framework
structure of MO
2, AlO
2 and PO
2 tetrahedral units. These as manufactured structures (which contain template prior
to calcination) can be represented by empirical chemical composition, on an anhydrous
basis, as:
mR: (M
xAl
yP
z)O
2
wherein "R" represents at least one organic templating agent present in the intracrystalline
pore system; "m" represents the moles of "R" present per mole of (M
xAl
yP
z)O
2, the maximum value in each case depending upon the molecular dimensions of the templating
agent and the available void volume of the pore system of the particular metal aluminophosphate
involved, "x", "y", and "z" represent the mole fractions of the metal "M", (i.e. magnesium,
manganese, zinc and cobalt), aluminum and phosphorus, respectively, present as tetrahedral
oxides.
[0057] The metal containing ALPOs are often referred to by the acronym as MeAPO. Also in
those cases where the metal "Me" in the composition is magnesium, the acronym MAPO
is applied to the composition. Similarly ZAPO, MnAPO and CoAPO are applied to the
compositions which contain zinc, manganese and cobalt respectively. To identify the
various structural species which make up each of the classes MAPO, ZAPO, CoAPO and
MnAPO, each species is assigned a number and is identified, for example, as ZAPO-5,
MAPO-11, CoAPO-34 and so forth.
[0058] The silicoaluminophosphate molecular sieves are synthesized by hydrothermal crystallization
methods generally known in the art. See, for example, U.S. Pat. Nos. 4,440,871; 4,861,743;
5,096,684; and 5,126,308, the methods of making of which are fully incorporated herein
by reference. A reaction mixture is formed by mixing together reactive silicon, aluminum
and phosphorus components, along with at least one template. Typically water or a
water/alcohol mixture is used as a solvent. Generally the mixture is sealed and heated,
preferably under autogenous pressure, to a temperature of at least 100°C, preferably
from 100°C to 250°C, until a crystalline product is formed. Formation of the crystalline
product can take anywhere from around 2 hours to as much as 2 weeks. In some cases,
stirring or seeding with crystalline material will facilitate the formation of the
product.
[0059] Typically, the molecular sieve precipitates from the process solution, which can
be the mother liquor. As a result of the crystallization or precipitation process,
the molecular sieve contains within its pores at least a portion of the template used
in making the initial reaction mixture. The crystalline structure of the sieve essentially
wraps around the template as it is formed. The template is then completely or partially
removed, thus generating an open pore structure.
[0060] In many cases, depending upon the nature of the final product formed, the template
may be too large to be eluted from the intracrystalline pore system. In such a case,
the template can be removed by a heat treatment process. For example, the template
can be calcined, or essentially combusted, in the presence of an oxygen-containing
gas, by contacting the template-containing sieve in the presence of the oxygen-containing
gas and heating at temperatures from 200°C to 900°C. In some cases, it may be desirable
to heat in an environment having a low oxygen concentration. In these cases, however,
the result will typically be a breakdown of the template into a smaller component,
rather than by the combustion process. This type of process can be used for partial
or complete removal of the template from the intracrystalline pore system. In other
cases, with smaller templates, complete or partial removal from the sieve can be accomplished
by conventional desorption processes such as those used in making standard zeolites.
[0061] The reaction mixture can contain one or more templates. Templates are structure directing
or affecting agents, and typically contain nitrogen, phosphorus, oxygen, carbon, hydrogen
or a combination thereof, and can also contain at least one alkyl or aryl group, with
1 to 8 carbons being present in the alkyl or aryl group. Mixtures of two or more templates
can also be used.
[0062] Representative templates include tetraethyl ammonium salts, cyclopentylamine, aminomethyl
cyclohexane, piperidine, triethylamine, cyclohexylamine, tri-ethyl hydroxyethylamine,
morpholine, dipropylamine (DPA), pyridine, isopropylamine and combinations thereof.
Preferred templates are triethylamine, cyclohexylamine, piperidine, pyridine, isopropylamine,
tetraethyl ammonium salts, dipropylamine, and mixtures thereof. The tetraethylammonium
salts include tetraethyl ammonium hydroxide (TEAOH), tetraethyl ammonium phosphate,
tetraethyl ammonium fluoride, tetraethyl ammonium bromide, tetraethyl ammonium chloride,
tetraethyl ammonium acetate. Preferred tetraethyl ammonium salts are tetraethyl ammonium
hydroxide and tetraethyl ammonium phosphate.
[0063] The SAPO molecular sieve structure can be effectively controlled using combinations
of templates. For example, in a particularly preferred embodiment, the SAPO molecular
sieve is manufactured using a template combination of TEAOH and dipropylamine. This
combination results in a particularly desirable SAPO structure for the conversion
of oxygenates, particularly methanol and dimethyl ether, to light olefins such as
ethylene and propylene.
[0064] The silicoaluminophosphate molecular sieve is typically admixed (i.e., blended) with
other materials. When blended, the resulting composition is typically referred to
as a SAPO catalyst, with the catalyst comprising the SAPO molecular sieve.
[0065] Once the first slurry of the present invention is prepared other materials can be
mixed with the molecular sieve. These materials include various inert or catalytically
active materials, or various binder materials, such as kaolin and other clays, various
forms of rare earth metals, metal oxides, other non-zeolite catalyst components, zeolite
catalyst components, alumina or alumina sol, titania, zirconia, magnesia, thoria,
beryllia, quartz, silica or silica sol, and mixtures thereof. These components are
also effective in reducing, inter alia, overall catalyst cost, acting as a thermal
sink to assit in heat shielding the catalyst during regeneration, densifying the catalyst
and increasing catalyst strength. It is particularly desirable that the inert materials
that are used in the catalyst to act as a thermal sink have a heat capacity of from
0.05 cal/g-°C to 1 cal/g-°C, more preferably from 0.1 cal/g-°C to 0.8 cal/g-°C, most
preferably from 0.1 cal/g-°C to 0.5 cal/g-°C.
[0066] The use of matrix materials such as naturally occurring clays,
e.g., bentonite and kaolin, improves the crush strength of the catalyst under commercial
operating conditions. Thus, the addition of clays improve upon the attrition resistance
or lifetime of the catalyst. The inactive materials also serve as diluents to control
the rate of conversion in a given process so that more expensive means for controlling
the rate of reaction is minimized. Naturally occurring clays which can be used in
the present invention include the montmorillonite and kaolin families which include
the subbentonites, and the kaolins, commonly known as Dixie, McNamee, Georgia and
Florida clays, or other in which the main mineral constituent is haloysite, kaolinite,
dickite, nacrite, or anauxite. Such clays can be used in the natural state or subjected
to calcination, acid treatment or chemical modification.
[0067] As with most catalysts clay is used in the invention as an inert densifier, and for
the most part the clay has no effect on catalytic activity or selectivity. In most
cases, the clay of choice is kaolin. Kaolin's ability to form pumpable, high solid
content slurries, low fresh surface area, and ease of packing because of its platelet
structure makes it particularly suitable for catalyst-processing. The preferred average
particle size of the kaolin is 0.1 µm to 0.6 µm with a D90 point of about 1 µm. The
iron and titania content of the clay can also be important. High iron or titania levels
can lead to undesirable secondary reactions. Because of environmental concerns, the
crystalline silica content of the clay has also become an important parameter.
[0068] Additional molecular sieve materials can be included as a part of the SAPO catalyst
composition or they can be used as separate molecular sieve catalysts in admixture
with the SAPO catalyst if desired. Structural types of small pore molecular sieves
that are suitable for use in this invention include AEI, AFT, APC, ATN, ATT, ATV,
AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU, PHI,
RHO, ROG, THO, and substituted forms thereof. Structural types of medium pore molecular
sieves that are suitable for use in this invention include MFI, MEL, MTW, EUO, MTT,
HEU, FER, AFO, AEL, TON, and substituted forms thereof. These small and medium pore
molecular sieves are described in greater detail in the
Atlas of Zeolite Structural Types, W.M. Meier and D.H. Olsen, Butterworth Heineman, 3rd ed., 1997, the detailed description
of which is explicitly incorporated herein by reference. Preferred molecular sieves
which can be combined with a silicoaluminophosphate catalyst include ZSM-5, ZSM-34,
erionite, and chabazite. The mixtures can be integrowths or mixtures of various crystalline
and/or amorphous phases, or physical mixtures of different molecular sieves.
[0069] The catalyst can be subjected to a variety of treatments to achieve the desired physical
and chemical characteristics. Such treatments include, but are not necessarily limited
to hydrothermal treatment, calcination, acid treatment, base treatment, milling, ball
milling, grinding, spray drying, and combinations thereof.
[0070] In this invention, a feed containing an oxygenate, and optionally a diluent or a
hydrocarbon added separately or mixed with the oxygenate, is contacted with a catalyst
containing a SAPO molecular sieve in a reaction zone or volume. The volume in which
such contact takes place is herein termed the "reactor," which may be a part of a
"reactor apparatus" or "reaction system." Another part of the reaction system may
be a "regenerator," which comprises a volume wherein carbonaceous deposits (or coke)
on the catalyst resulting from the olefin conversion reaction are removed by contacting
the catalyst with regeneration medium.
[0071] The oxygenate feedstock of this invention comprises at least one organic compound
which contains at least one oxygen atom, such as aliphatic alcohols, ethers, carbonyl
compounds (aldehydes, ketones, carboxylic acids, carbonates, esters and the like).
When the oxygenate is an alcohol, the alcohol can include an aliphatic moiety having
from 1 to 10 carbon atoms, more preferably from 1 to 4 carbon atoms. Representative
alcohols include but are not necessarily limited to lower straight and branched chain
aliphatic alcohols and their unsaturated counterparts. Examples of suitable oxygenate
compounds include, but are not limited to: methanol; ethanol; n-propanol; isopropanol;
C
4 - C
20 alcohols; methyl ethyl ether; dimethyl ether; diethyl ether; di-isopropyl ether;
formaldehyde; dimethyl carbonate; dimethyl ketone; acetic acid; and mixtures thereof.
Preferred oxygenate compounds are methanol, dimethyl ether, or a mixture thereof.
[0072] The method of making the preferred olefin product in this invention can include the
additional step of making these compositions from hydrocarbons such as oil, coal,
tar sand, shale, biomass and natural gas. Methods for making the compositions are
known in the art. These methods include fermentation to alcohol or ether, making synthesis
gas, then converting the synthesis gas to alcohol or ether. Synthesis gas can be produced
by known processes such as steam reforming, autothermal reforming and partial oxidization.
[0073] One or more inert diluents may be present in the feedstock, for example, in an amount
of from 1 to 99 molar percent, based on the total number of moles of all feed and
diluent components fed to the reaction zone (or catalyst). As defined herein, diluents
are compositions which are essentially non-reactive across a molecular sieve catalyst,
and primarily function to make the oxygenates in the feedstock less concentrated.
Typical diluents include, but are not necessarily limited to helium, argon, nitrogen,
carbon monoxide, carbon dioxide, water, essentially non-reactive paraffins (especially
the alkanes such as methane, ethane, and propane), essentially non-reactive alkylenes,
essentially non-reactive aromatic compounds, and mixtures thereof. The preferred diluents
are water and nitrogen. Water can be injected in either liquid or vapor form.
[0074] Hydrocarbons can also be included as part of the feedstock, i.e., as co-feed. As
defined herein, hydrocarbons included with the feedstock are hydrocarbon compositions
which are converted to another chemical arrangement when contacted with molecular
sieve catalyst. These hydrocarbons can include olefins, reactive paraffins, reactive
alkylaromatics, reactive aromatics or mixtures thereof. Preferred hydrocarbon co-feeds
include, propylene, butylene, pentylene, C
4+ hydrocarbon mixtures, C
5+ hydrocarbon mixtures, and mixtures thereof. More preferred as co-feeds are a C
4+ hydrocarbon mixtures, with the most preferred being C
4+ hydrocarbon mixtures which are obtained from separation and recycle of reactor product.
[0075] In the process of this invention, coked catalyst can be regenerated by contacting
the coked catalyst with a regeneration medium to remove all or part of the coke deposits.
This regeneration can occur periodically within the reactor by ceasing the flow of
feed to the reactor, introducing a regeneration medium, ceasing flow of the regeneration
medium, and then reintroducing the feed to the fully or partially regenerated catalyst.
Regeneration may also occur periodically or continuously outside the reactor by removing
a portion of the deactivated catalyst to a separate regenerator, regenerating the
coked catalyst in the regenerator, and subsequently reintroducing the regenerated
catalyst to the reactor. Regeneration can occur at times and conditions appropriate
to maintain a desired level of coke on the entire catalyst within the reactor.
[0076] Catalyst that has been contacted with feed in a reactor is defined herein as "feedstock
exposed." Feedstock exposed catalyst will provide olefin conversion reaction products
having substantially lower propane and coke content than a catalyst which is fresh
and regenerated. A catalyst will typically provide lower amounts of propane as it
is exposed to more feed, either through increasing time at a given feed rate or increasing
feed rate over a given time.
[0077] Any standard reactor system can be used, including fixed bed, fluid bed or moving
bed systems. Preferred reactors are co-current riser reactors and short contact time,
countercurrent free-fall reactors. Desirably, the reactor is one in which an oxygenate
feedstock can be contacted with a molecular sieve catalyst at a weight hourly space
velocity (WHSV) of at least about 1 hr
-1, preferably in the range of from 1 hr
-1 to 1000 hr
-1, more preferably from 10 hr
-1 to 1000 hr
-1, and most preferably from 20 hr
-1 to 200 hr
-1. WHSV is defined herein as the weight of oxygenate, and hydrocarbon which may optionally
be in the feed, per hour per weight of the molecular sieve content of the catalyst.
Because the catalyst or the feedstock may contain other materials which act as inerts
or diluents, the WHSV is calculated on the weight basis of the oxygenate feed, and
any hydrocarbon which may be present, and the molecular sieve contained in the catalyst.
[0078] Preferably, the oxygenate feed is contacted with the catalyst when the oxygenate
is in a vapor phase. Alternately, the process may be carried out in a liquid or a
mixed vapor/liquid phase. When the process is carried out in a liquid phase or a mixed
vapor/liquid phase, different conversions and selectivities of feed-to-product may
result depending upon the catalyst and reaction conditions. The process can generally
be carried out at a wide range of temperatures. An effective operating temperature
range can be from 200°C to 700°C, preferably from 300°C to 600°C, more preferably
from 350°C to 550°C.
[0079] The conversion of oxygenates to produce light olefins may be carried out in a variety
of catalytic reactors. Reactor types include fixed bed reactors, fluid bed reactors,
and concurrent riser reactors. Additionally, countercurrent free fall reactors may
be used in the conversion process as described in US-A-4,068,136, the detailed description
of which is expressly incorporated herein by reference.
[0080] In a preferred embodiment of the continuous operation, only a portion of the catalyst
is removed from the reactor and sent to the regenerator to remove the accumulated
coke deposits that result during the catalytic reaction. In the regenerator, the catalyst
is contacted with a regeneration medium containing oxygen or other oxidants. Examples
of other oxidants include O
3, SO
3, N
2O, NO, NO
2, N
2O
5, and mixtures thereof. It is preferred to supply O
2 in the form of air. The air can be diluted with nitrogen, CO
2, or flue gas, and steam may be added. Desirably, the O
2 concentration in the regenerator is reduced to a controlled level to minimize overheating
or the creation of hot spots in the spent or deactivated catalyst. The deactivated
catalyst also may be regenerated reductively with H
2, CO, mixtures thereof, or other suitable reducing agents. A combination of oxidative
regeneration and reductive regeneration can also be employed.
[0081] In essence, the coke deposits are removed from the catalyst during the regeneration
process, forming a regenerated catalyst. The regenerated catalyst is then returned
to the reactor for further contact with feed. Typical regeneration temperatures are
in the range of 250°C to 700°C, desirably in the range of 350°C to 700°C. Preferably,
regeneration is carried out at a temperature range of 450°C to 700°C.
[0082] In one embodiment, the reactor and regenerator are configured such that the feed
contacts the regenerated catalyst before it is returned to the reactor. In an alternative
embodiment, the reactor and regenerator are configured such that the feed contacts
the regenerated catalyst after it is returned to the reactor. In yet another embodiment,
the feed stream can be split such that feed contacts regenerated catalyst before it
is returned to the reactor and after it has been returned to the reactor.
[0083] One skilled in the art will also appreciate that the olefins produced by the oxygenate-to-olefin
conversion reaction of the present invention can be polymerized to form polyolefins,
particularly polyethylene and polypropylene. Processes for forming polyolefins from
olefins are known in the art. Catalytic processes are preferred. Particularly preferred
are metallocene, Ziegler/Natta and acid catalytic systems. See, for example, U.S.
Patent Nos. 3,258,455; 3,305,538; 3,364,190; 5,892,079; 4,659,685; 4,076,698; 3,645,992;
4,302,565; and 4,243,691, the catalyst and process descriptions of each being expressly
incorporated herein by reference. In general, these methods involve contacting the
olefin product with a polyolefin-forming catalyst at a pressure and temperature effective
to form the polyolefin product.
[0084] A preferred polyolefin-forming catalyst is a metallocene catalyst. The preferred
temperature range of operation is from 50°C to 240°C and the reaction can be carried
out at low, medium or high pressure, being anywhere within the range of about 1 bar
to 200 bars. For processes carried out in solution, an inert diluent can be used,
and the preferred operating pressure is from 10 0 bars to 150 bars, with a preferred
temperature of 120°C to 230°C. For gas phase processes, it is preferred that the temperature
generally be from 60°C to 160°C, and that the operating pressure be from 5 bars to
50 bars.
[0085] In addition to polyolefins, numerous other olefin derivatives may be formed from
the olefins recovered therefrom. These include, but are not limited to, aldehydes,
alcohols, acetic acid, linear alpha olefins, vinyl acetate, ethylene dicholoride and
vinyl chloride, ethylbenzene, ethylene oxide, cumene, isopropyl alcohol, acrolein,
allyl chloride, propylene oxide, acrylic acid, ethylene-propylene rubbers, and acrylonitrile,
and trimers and dimers of ethylene, propylene or butylenes. The methods of manufacturing
these derivatives are well known in the art, and therefore, are not discussed herein.
[0086] This invention will be better understood with reference to the following examples,
which are intended to illustrate specific embodiments within the overall scope of
the invention as claimed.
Example
[0087] A four tube microfiltration (MF) apparatus was used to concentrate a tank of SAPO-34
synthesis slurry. The apparatus comprised a 100 gal feed tank, a centrifugal pump
with nominal recirculation rate of 30 gal/min, a four tube microfilter each tube of
approximately 1.9 cm in diameter and 3 m long and having a surface area of about 2
ft
2, and a permeate collection barrel. The tubes were made of polymeric MF tubes (Koch
HFP-276 PVE)
[0088] Deionized water was added to synthesis slurry in the feed tank
28. The slurry
30 was pumped out of the feed tank
28 with pump
31 at a discharge pressure of 90 ± 5 psig and through a microfilter
18 having 4 tube-and-shell type filter channels
20. The concentrated slurry was directed back to the feed tank
28, while the permeate stream containing water and other components was directed to tank
34. Temperature of the slurry was maintained between 50°C and 55°C after an initial
startup period and the permeate flow rate ranged from about 1.8 to 3.0 liters/min.
[0089] The starting concentration was approximately 12.5% solids on a dry basis with the
liquid portion containing water, unreacted template, tetraethylammonium hydroxide
(TEOH) and unflashed dipropylamine, and an unanalyzed mixture of unreacted starting
materials containing, aluminum, phosphorus and silica, and byproducts from the synthesis.
The starting slurry weighed 440 lbs with a calculated solids content of 55 lbs. The
final slurry concentrate was measured to have a dry solids content of 28.4 wt%. No
solids were observed to pass through with the permeate. The conductivity of the permeate
was reduced from greater than 10,000 µmho to less than 500 µmho after a total of 3.9
lbs of wash water per Ib of slurry was added over a 10 hour period. A total of about
600 kg of deionized water were used to wash 200 kg of initial slurry. The permeate
was collected and the TEOH concentrated from the water with a nanofilter and recycled
back to the reactor.
[0090] Having now fully described this invention, it will be appreciated by those skilled
in the art that the invention can be performed within a wide range of parameters within
what is claimed, without departing from the spirit and scope of the invention.
1. Verfahren zur Herstellung eines Molekularsiebkatalysators, bei dem
i) man eine konzentrierte Molekularsiebaufschlämmung, die Molekularsieb und ein Fluid
enthält, nach dem Verfahren herstellt, bei dem
a) man eine Molekularsiebaufschlämmung, die Molekularsiebpartikel, die Herstellungsmischung
und ein Fluid enthält, in das vordere Ende von mindestens einem Mikrofilterkanal einbringt,
der Poren aufweist,
b) man die Aufschlämmung durch den Mikrofilterkanal leitet und das die Poren des Mikrofilterkanals
passierende Permeat abtrennt, um die Aufschlämmung zu konzentrieren, und
c) man am rückwärtigen Ende des Mikrofilterkanals eine konzentrierte Molekularsiebaufschlämmung
gewinnt,
ii) man die konzentrierte Molekularsiebaufschlämmung mit einem Bindemittel mischt,
um eine Katalysatoraufschlämmung zu bilden,
iii) man die Katalysatoraufschlämmung in eine Formungsanlage führt,
iv) man Katalysatorpartikel gewinnt.
2. Verfahren nach Anspruch 1, bei dem das Fluid Wasser ist.
3. Verfahren nach Anspruch 1 oder 2, das ferner die Stufen aufweist, in denen man d)
Waschfluid zu der Molekularsiebaufschlämmung gibt, e) man die Molekularsiebaufschlämmung
und das Waschfluid in einem Wartetank mischt, f) man die Molekularsiebaufschlämmung
durch das vordere Ende von mindestens einem Mikrofilterkanal injiziert, der Poren
aufweist, und das die Poren des Mikrofilters passierende Permeat abtrennt.
4. Verfahren nach Anspruch 3, bei dem die Stufen d), e) und f) wiederholt werden, bis
die Molekularsiebaufschlämmung den gewünschten Reinheitsgrad hat.
5. Verfahren nach Anspruch 3 oder 4, bei dem die Stufen d), e) und f) wiederholt werden,
bis das die Poren passierende Permeat eine Leitfähigkeit von 50 µmho/cm bis 5000 µmho/cm
hat.
6. Verfahren nach einem der Ansprüche 3 bis 5, bei dem das Waschfluid Wasser, ein Alkohol
oder eine Mischung davon ist.
7. Verfahren nach einem der Ansprüche 3 bis 6, bei dem die Stufen d), e) und f) kontinuierlich
durchgeführt werden.
8. Verfahren nach Anspruch 7, bei dem das Waschfluid die Molekularsiebaufschlämmung von
der Rückseite des Mikrofilterkanals kontaktiert.
9. Verfahren nach einem der Ansprüche 3 bis 8, bei dem man die Zugabe des Waschfluids
durchführt, während die Molekularsiebaufschlämmung konzentriert wird.
10. Verfahren nach Anspruch 1 bis 9, bei dem man das in den Stufen b) und/oder f) abgetrennte
Permeat mit einem Nanofilter konzentriert, um ein konzentriertes Permeat zu ergeben,
und man es in einem Verfahren zur Herstellung eines Molekularsiebs verwendet.
11. Verfahren nach Anspruch 10, bei dem der Nanofilter ein poröses Material mit nominellem
Porendurchmesser von 0,5 bis 10 Nanometern enthält.
12. Verfahren nach Anspruch 1 bis 11, bei dem die in Stufe a) verwendete Molekularsiebaufschlämmung
das Permeat der Filtration einer Molekularsiebherstellungsmischung unter Verwendung
eines Makrofilters ist.
13. Verfahren nach Anspruch 12, bei dem der Makrofilter eine nominelle Porenöffnung größer
als 10 µm hat.
14. Verfahren nach Anspruch 1 bis 13, bei dem der Anfangsfeststoffgehalt des Molekularsiebs
in der Herstellungsaufschlämmung zwischen 5 Gew.% und 30 Gew.% liegt.
15. Verfahren nach Anspruch 1 bis 14, bei dem der Feststoffgehalt der konzentrierten Molekulargewichtsaufschlämmung
zwischen 20 Gew.% und 60 Gew.%, vorzugsweise zwischen 25 Gew.% und 40 Gew.% liegt.
16. Verfahren nach Anspruch 1 bis 15, bei dem die Molekularsiebaufschlämmung Molekularsiebpartikel
mit einem durchschnittlichen Partikeldurchmesser von weniger als 5 µm enthält.
17. Verfahren nach Anspruch 1 bis 16, bei dem das Molekularsieb ausgewählt ist aus SAPO-17,
SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-47, ALPO-5, ALPO-11, ALPO-18, ALPO-34, ALPO-36,
ALPO-37, ALPO-46, metallhaltigen Formen und Mischungen davon.
18. Verfahren nach Anspruch 1 bis 17, bei dem der Mikrofilter ein poröses Material mit
nominellen Porenöffnungen von etwa 0,05 µm bis 10 µm enthält.
19. Verfahren nach Anspruch 1 bis 18, bei dem der Mikrofilter Rohr-und-Mantel-Mikrofilterkanäle
enthält.
20. Verfahren nach Anspruch 1 bis 19, bei dem das Bindemittel ausgewählt ist aus der Gruppe
bestehend aus Aluminiumoxid, Siliciumdioxid-Aluminiumoxid und Siliciumdioxid.
21. Verfahren nach Anspruch 1 bis 19, bei dem das Bindemittel peptisiertes Aluminiumoxid
und/oder Aluminiumchlorhydrol ist.
22. Verfahren nach Anspruch 1 bis 21, bei dem das Bindemittel in der Menge von 5 Gew.%
bis 20 Gew.% vorhanden ist, bezogen auf das Gewicht des Katalysators nach der Calcinierung.
23. Verfahren nach Anspruch 1 bis 22, das ferner die Stufe aufweist, in der man (v) die
konzentrierte Molekularsiebaufschlämmung oder Katalysatoraufschlämmung mit einer Matrix
mischt.
24. Verfahren nach Anspruch 23, bei dem Stufen (ii) und (v) simultan stattfinden.
25. Verfahren nach Anspruch 23 oder 24, bei dem die Menge der Matrix 40 Gew.% bis 90 Gew.%
beträgt, bezogen auf das Gesamtgewicht des Katalysators nach der Calcinierung.
26. Verfahren nach Anspruch 1 bis 25, bei dem die Formungsanlage ausgewählt ist aus einer
Extrusionsanlage, einer Pelletieranlage oder einem Sprühtrockner.
27. Verfahren nach Anspruch 26, bei dem die Formungsanlage ein Sprühtrockner ist.
1. Procédé de préparation d'un catalyseur à tamis moléculaire, comprenant les étapes
consistant à :
i) préparer une suspension concentrée de tamis moléculaire contenant un tamis moléculaire
et un fluide au moyen du procédé comprenant les étapes consistant à :
a) introduire une suspension de tamis moléculaire contenant des particules de tamis
moléculaire, le mélange de préparation et un fluide dans l'extrémité frontale d'au
moins un canal d'un microfiltre comprenant des pores ;
b) faire passer la suspension à travers le canal du microfiltre et séparer le perméat
traversant les pores du canal du microfiltre pour concentrer la suspension ; et
c) recueillir une suspension concentrée de tamis moléculaire par l'extrémité arrière
du canal du microfiltre ;
ii) mélanger la suspension concentrée de tamis moléculaire avec un liant pour former
une suspension de catalyseur ;
iii) diriger la suspension de catalyseur vers une unité de façonnage ;
iv) recueillir les particules de catalyseur.
2. Procédé selon la revendication 1, dans lequel le fluide est de l'eau.
3. Procédé selon la revendication 1 ou 2, comprenant, en outre, les étapes de d) addition
d'un fluide de lavage à la suspension de tamis moléculaire, e) mélange de la suspension
de tamis moléculaire et du fluide de lavage dans une cuve de garde, f) injection de
la suspension de tamis, moléculaire dans l'extrémité frontale d'au moins un canal
d'un microfiltre comprenant des pores et séparation du perméat traversant les pores
du microfiltre.
4. Procédé selon la revendication 3, dans lequel on recommence les étapes d), e) et f)
jusqu'à ce que la suspension de tamis moléculaire ait le taux désiré de pureté.
5. Procédé selon la revendication 3 ou 4, dans lequel on recommence les étapes d), e)
et f) jusqu'à ce que le perméat traversant les pores ait une conductivité de 50 µmho/cm
à 5000 µmho/cm.
6. Procédé selon l'une quelconque des revendications 3 à 5, dans lequel le fluide de
lavage est de l'eau, un alcool ou un mélange de ceux-ci.
7. Procédé selon l'une quelconque des revendications 3 à 6, dans lequel on effectue les
étapes d), e) et f) en continu.
8. Procédé selon la revendication 7, dans lequel le fluide de lavage vient au contact
de la suspension de tamis moléculaire par l'arrière du canal du microfiltre.
9. Procédé selon l'une quelconque des revendications 3 à 8, dans lequel on effectue l'addition
du fluide de lavage quand la suspension de tamis moléculaire est concentrée.
10. Procédé selon les revendications 1 à 9, dans lequel on concentre le perméat séparé
lors des étapes b) et/ou f) avec un nanofiltre de façon à obtenir un perméat concentré
et on l'utilise dans un procédé de fabrication d'un tamis moléculaire.
11. Procédé selon la revendication 10, dans lequel le nanofiltre contient une matière
poreuse ayant un diamètre nominal des pores de 0,5 à 10 nanomètres.
12. Procédé selon les revendications 1 à 11, dans lequel la suspension de tamis moléculaire
utilisée dans l'étape a) est le perméat de la filtration d'un mélange de préparation
de tamis moléculaire en utilisant un macrofiltre.
13. Procédé selon la revendication 12, dans lequel le macrofiltre a une ouverture nominale
des pores supérieure à 10 micromètres.
14. Procédé selon les revendications 1 à 13, dans lequel la teneur initiale en solides
du tamis moléculaire dans la suspension de préparation est comprise entre 5 % et 30
% en poids.
15. Procédé selon les revendications 1 à 14, dans lequel la teneur en solides de la suspension
concentrée de tamis moléculaire est comprise entre 20 % et 60 % en poids, de préférence
entre 25 % et 40 % en poids.
16. Procédé selon les revendications 1 à 15, dans lequel la suspension de tamis moléculaire
contient des particules de tamis moléculaire ayant un diamètre moyen des particules
inférieur à 5 micromètres.
17. Procédé selon les revendications 1 à 16, dans lequel on choisit le tamis moléculaire
parmi SAPO-17, SAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-47, ALPO-5, ALPO-11, ALPO-18,
ALPO-34, ALPO-36, ALPO-37, ALPO-46, des formes de ceux-ci contenant un métal et des
mélanges de ceux-ci.
18. Procédé selon les revendications 1 à 17, dans lequel le microfiltre comprend une matière
poreuse ayant des ouvertures nominales des pores d'environ 0,05 micromètre à 10 micromètres.
19. Procédé selon les revendications 1 à 18, dans lequel le microfiltre comprend des canaux
de microfiltre à tube et enveloppe.
20. Procédé selon les revendications 1 à 19, dans lequel le liant est choisi dans l'ensemble
constitué d'alumine, de silice-alumine et de silice.
21. Procédé selon les revendications 1 à 19, dans lequel le liant est de l'alumine peptisée
et/ou du chlorhydrol aluminique.
22. Procédé selon les revendications 1 à 21, dans lequel le liant est présent en une quantité
de 5 % à 20 % en poids par rapport au poids du catalyseur après calcination.
23. Procédé selon les revendications 1 à 22, comprenant, en outre, l'étape consistant
à (v) mélanger la suspension concentrée de tamis moléculaire ou la suspension de catalyseur
avec une matrice.
24. Procédé selon la revendication 23, dans lequel on effectue simultanément les étapes
ii) et (v).
25. Procédé selon la revendication 23 ou 24, dans lequel la matrice représente de 40 %
à 90 % en poids par rapport au poids total de catalyseur après calcination.
26. Procédé selon les revendications 1 à 25, dans lequel l'unité de façonnage est choisie
parmi une unité d'extrusion, une unité de transformation en granules et un séchoir
par pulvérisation.
27. Procédé selon la revendication 26, dans lequel l'unité de façonnage est un séchoir
par pulvérisation.